As those skilled in the art know, the cost-effectiveness of certain satellite data transmission (or collection) applications requires the satellites to have very large transmission capabilities in terms of bit rate. Such is notably the case with the so-called “broadband” multimedia applications, which often require capabilities of the order of several tens of gigabits per second.
Today, the frequency bandwidths that are allocated to the (tele)communication satellites are insufficient to allow them to reach such capacities.
To improve the situation, a frequency re-use technique is applied consisting, on the one hand, in subdividing the service area that the satellite must cover into cells, each of which is assigned a sub-bandwidth equal to a fraction of the bandwidth that is allocated to the service concerned, and on the other hand, in assigning identical sub-bandwidths to cells that are sufficiently well isolated from each other. By defining regular cell patterns, it is possible to re-use a number of sub-bandwidths several times, so making it possible to multiply, sometimes by several tens, the frequency resources.
However, this technique of frequency re-use by means of regular patterns presents a number of drawbacks.
A first drawback is the lack of flexibility. In practice, the dimensions and the position of each cell are fixed, and each cell is definitively allocated a sub-bandwidth. Consequently, any desire to modify the dimensions of a cell or the width of its sub-bandwidth will disrupt all the cells that use the same sub-bandwidth and therefore all the frequency allocation system, which means completely redefining the allocation.
A second drawback stems from the lack of flexibility. In practice, the cells that have traffic below the average waste frequency, whereas those that could have traffic greater than the average cannot obtain the frequency resources that would make it possible to satisfy the demand. This waste of frequency is both structural, since it results from a long term traffic planning, and cyclical, since it results from the failure to take into account short term traffic variations in time (for example, between day and night) and in space (for example because of local events).